Posted
by
samzenpus
on Wednesday January 23, 2013 @11:15PM
from the turn-out-the-lights dept.

skade88 writes "NPR is reporting on a study in which the author claims to have found the formula to predict the average life span of members of a species. It does not apply to specific individuals of that species, only to the average life span of members of the species as a whole. From the article: 'It's hard to believe that creatures as different as jellyfish and cheetahs, daisies and bats, are governed by the same mathematical logic, but size seems to predict lifespan. The formula seems to be nature's way to preserve larger creatures who need time to grow and prosper, and it not only operates in all living things, but even in the cells of living things. It tells animals for example, that there's a universal limit to life, that though they come in different sizes, they have roughly a billion and a half heart beats; elephant hearts beat slowly, hummingbird hearts beat fast, but when your count is up, you are over.'"

The 1960's was "a long time ago"? We have a much more accurate value than Asimov's in Genesis 6:3, applying to all the billions of human lives since, and verifiably correct to the two significant digits of precision indicated.

In terms of specific methodology to arrive at that figure, though, I cannot say beyond the obvious.;)

the summary says that the result is valid for species, not individuals. even that is wrong; it's not exactly valid for every species; the result is actually that there is a significant power-law trend across species which is that the mortality rate and birth rate both scale approximately as -0.25*(dry mass) on a log-log scale. however there is also significant variation from the log-log line-of-best-fit; the r^2 is around 0.8, though i don't care enough to read exactly how they designed the study. http://www.pnas.org/content/104/40/15777.full [pnas.org]

humans have, of course, cheated death to some extent, so we're outliers, though it is worth noting that prehistoric humans had a max. lifespan of around 40 years...

this is an old result for animal species; the `result' here is that they checked the extrapolated fit for ~700 plant species and validated it in that domain. scientists generally make small extensions or validate previous conjectures; since the public doesn't understand what they're building from, the media has to present the history as the novelty. it's kind of funny, really.

i remember reading a paper (from sante fe institute, of course) ~20 years ago or so which tried to define a `generalized heartbeat' for cities and nation-states to see if the scaling law would extrapolate. of course, the problem is you can define such a thing however you want.

There are so many exceptions to this "rule" that it is at best an interesting pattern. There are big turtles that live great long lives and big turtles that don't with little turtles being all over the place as well. There are birds of all kinds of sizes with small birds that live 80 years and big birds that live under 20. Some bacteria seem to be nearly immortal and others live days. Within dogs the big ones hardly outlast green bananas while the little ratty ones go on for decades. Poplar trees grow huge and die fast, oaks go on and on but some smaller trees are thousands of years old.

Even humming birds live a few years at crazy heartbeats as high as 1200 bpm (look it up if you don't buy that mind blowing number) yet other bigger birds with much slower heart beats live for the same length of time. So it isn't size or heartbeats.

If I had to suspect anything lifespan will be an evolutionary advantage like anything else. If you are surrounded by ever changing dangers a short fast life-cycle is probably best. But if you are fairly safe in steady environment a long life is probably safer. Turtles have slow metabolisms which allow them to survive long periods without food and are fairly safe from predictors so they don't have to worry about adapting too much. Rabbits are basically the forest's McNuggets so they need to continuously adapt in numbers and probably other things such as coloring; hence a fast short life cycle. We have created civilization where we are nearly 100% safe from predators and with things like food storage are not so buffeted by a changing nature; so we are getting longer an longer lived.

Even if there was a hard quota on how many heartbeats you had, there's no point saving up your heartbeats not exercising just to die early from a heart attack.

Actually, I don't exercise for crap, I'm overweight, and my resting heart rate is riduclously high. Sure, exercise would get my heart rate up in the short term, but if I had a stronger, more athletic heart, built through exercising, I would conserve heartbeats over time. Mom was very athletic, and her resting heart rate was something scary slow.